1. Field of the Invention
The present invention relates in general to access control systems, and more specifically to an apparatus for optically reading key units having a code pattern thereon and allowing access when the proper code is detected.
2. Description of the Prior Art
It is well known that mechanical locks have security disadvantages in that these locks can be opened by unauthorized persons having some expertise in this field. Even most electromechanical locks that are presently available have not completely solved this problem. These units still require that an opening or slot be provided within which the key must be positioned before the lock will allow access. See, e.g., U.S. Pat. No. 3,797,936 issued to Dimitriadis on March 19, 1974. One system has been provided that allows remote sensing of a key without the need of a key slot or opening. This system detects the key as the key is brought into a zone containing an electromagnetic field. See, e.g., U.S. Pat. No. 3,732,465 issued to Palmer et al on May 8, 1973. However, such systems have tended to be electromagnetic noise sensitive, and have been found to be somewhat limited in terms of the number of code combinations available for use.
Optical scanning systems have been developed for optically reading keys. However, these systems have been found to have deficiences, as above, in terms of requiring a key slot. More importantly, even optical scanners having a surface and not a slot for a key require that the key be placed on the surface before scanning by the apparatus is possible. Optical scanners for reading printed code patterns on various objects without requiring that the codes have a particular orientation have only recently been developed (see, e.g. U.S. Pat. Nos. 3,662,758 issued to Schanne on Nov. 23, 1971; 3,676,645 issued to Fickenscher on July 11, 1972; 3,818,444 issued to Connell on June 18, 1974; and 3,735,096 issued to Knockeart on May 22, 1973). These scanners use a non-divergent or coherent light source such as a laser beam. Product identification is the only present application for such optical scanners known to the applicant. No optical reader for door access control has been found wherein the reading of an object having a code pattern thereon is allowed notwithstanding the randomness of the placement of the key unit with respect to the scanning surface.